Nonlinear Site Response: Where We're At (A report from a SCEC/PEER seminar and workshop)

Although the fact that sediments can amplify earthquake ground motion was recognized at least 100 years ago (Milne, 1898), there has been a lingering uncertainty as to whether the degree of amplification varies with the level of input motion. This issue remains as one of the most important questions with respect to understanding and predicting earthquake ground motion. In accordance with the conservation of energy, seismicwave amplitudes generally increase in sediments due to lower densities and and/or lower seismic velocities. In addition, resonance effects can occur where abrupt impedance contrasts exist. If sediments were perfectly elastic, their response would be independent of incident-wave amplitudes. As with any real material, however, sediments begin to yield at some level of strain, and this violation of Hooke's law will give rise to a nonlinear response. The engineering community has long believed that sediment nonlinearity is significant. This perspective was based almost entirely on...